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https://issues.apache.org/jira/browse/HADOOP-4813?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12655044#action_12655044
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Doug Cutting commented on HADOOP-4813:
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As a related matter, I'd like to change the underlying IPC layer to take,
instead of a Writable a List<ByteBuffer> for requests and return a ByteBuffer
for responses. Then we can layer an RPC implementation on top that does not
copy buffers but rather assembles a list of them. The simplest implementation
would allocate new buffers per request, then let them get GC'd. Such request
and response buffers should be short-lived and cheap to GC, but if that proves
to be a problem we could consider pooling them.
> Avoid a buffer copy while replying to RPC requests.
> ---------------------------------------------------
>
> Key: HADOOP-4813
> URL: https://issues.apache.org/jira/browse/HADOOP-4813
> Project: Hadoop Core
> Issue Type: Improvement
> Components: ipc
> Reporter: Raghu Angadi
>
> RPC server first serializes RPC response to a ByteArrayOutputStream and then
> creates a new array to write to socket. For most responses the RPC handler is
> able to write the entire response in-line. If we could use the same buffer
> used by ByteArrayOutputStream, we can avoid this copy.
> As mentioned in HADOOP-4802, yet another copy could be avoided (in most
> cases) if we use a static direct buffer for the responses (not proposed for
> this jira).
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